Now a lawsuit filed by three King County taxpayers, including a retired Seattle assistant city attorney, alleges the purchase was illegal. The plaintiffs say port officials overstepped their authority by purchasing the 42-mile Eastside rail corridor and misused port tax money to buy it from BNSF Railway Company.

The lawsuit -- filed by Arthur Lane, John Allerton, and Kenneth Gorohoff in King County Superior Court -- seeks to reverse the sale and refund any tax money used to pay for it. According to the lawsuit, state law prohibits port districts from purchasing rail lines outside the boundaries unless necessary to link the Port's freight lines to the interstate rail system. In this case, the rail line extends into Snohomish County and freight shipped to and from the Port of Seattle is hauled via other rail lines, according to the lawsuit.

Officials have considered a number of uses for the corridor, including interurban commuter trains coupled with trails for bicyclists and pedestrians. Sound Transit has studied running light rail along portions of the corridor.

While the Port may have had good intentions, the plaintiffs argue the purchase failed to comply with state law, said David Jurca, their attorney.

"It's a business that we think the Port of Seattle has no business being involved in," he said last week. "It takes money out of the Port's coffers that taxpayers have to fill up."

The lawsuit, filed in July, still is in the early stages, he said.

In a response to the lawsuit filed in court, the Port's lawyers said the acquisition was "fully within the Port of Seattle authority."

The Port's lawyers say it "preserves a substantial and irreplaceable asset that will allow the Port of Seattle and other regional partners to address the region's growing transportation needs, provides a necessary link to an interstate railroad system, and provides an essential alternative transportation corridor in case of a natural or manmade disaster."

Former King County Executive Ron Sims first proposed bringing the BNSF corridor into public ownership to prevent developers from buying it in pieces. But King County couldn't afford the transaction on its own, so the county turned to the Port and other regional stakeholders for help.

The Port purchased the northern half of the corridor between Woodinville and south Snohomish County after several years of negotiations. In addition, BNSF donated the southern portion from Woodinville to Renton, which was valued at $327 million. Under a Memorandum of Understanding, other stakeholders, including Sound Transit, the City of Redmond, the Cascade Water Alliance, and Seattle Public Utilities, would negotiate for future ownership of parts of the corridor.

"We've never seen ourselves as long-term owners of the corridor," Port spokeswoman Charla Skaggs said.

King County paid $1.9 million to the Port for an easement to develop a 26-mile trail along the southern segment. The southern half of the line also included a spur to Redmond, which port officials have sold to the city for $10 million, according to the lawsuit.

Prior to the deal, the Port held several public meetings and received no formal complaints questioning the legality of the purchase, Skaggs said.

Lane, a retired Seattle assistant city attorney and former consultant to City Light, and Gorohoff, a former City Light employee, were party to a series of lawsuits a few years ago that won large rebates for utility customers. They challenged the way the city of Seattle charged utility customers to pay for the maintenance of streetlights and fire hydrants, arguing the charges were illegal because ratepayers were being asked to pay for something that didn't uniquely benefit them.

In both cases, the courts ruled against the city and ordered million of dollars in rebates to utility customers.

"We're not community activists. We just looked at the law," Lane said in a recent telephone interview.

The lawsuit, which seeks class-action status, names the Port, King County, BNSF, Redmond, and GNP Rly, Inc., as defendants. GNP was hired by the Port to operate and maintain a short-line freight service along the northern corridor. Before BNSF announced it was selling the corridor in 2003, it operated a small freight line for local industries, including Boeing.